18.1 Options

There are many options available for explicitly correlated methods, but sensible defaults are
used for all of them. For details see the MOLPRO reference manual.
The most important options are:

DF_BASIS=basis

Select the
basis for density fitting (see section 16 for details).
basis can either refer to a set name defined in the basis block,
or to a default MP2 fitting basis (e.g., DF_BASIS=VTZ generates
the VTZ/MP2FIT basis). By default, the MP2FIT basis that corresponds to the
orbital basis is used.

RI_BASIS=basis

Select the
basis for the resolution of the identity (RI).
By default the JKFIT basis that corresponds to the chosen orbital basis is used.
In conjunction with the VnZ-F12 basis sets, it is recommended to use the
VnZ-F12/OPTRI sets of Yousaf and Peterson, J. Chem. Phys. 129, 18410 (2008).

ANSATZ=ansatz

Select the explicitly correlated ansatz
ansatz methods. See section 18.3 for the defaults and the MOLPRO
manual for further details and possibilities. Normally the defaults hould be used
[3C(FIX) for canonical methods and 3*A(LOC) for local methods].

GEM_BETA=value

Exponent for Slater-type frozen geminal (default 1.0 ).

SINGLES=0

Disable CABS singles correction. The default is SINGLES=1.

In the following, we briefly summarize the meaning of these options and of the approximations that can be used.
For more details and further references to related work of other authors see H.-J. Werner, T. B. Adler, and F. R. Manby,
General orbital invarient MP2-F12 theory, J. Chem. Phys. 126, 164102 (2007) and
G. Knizia and T. B. Adler and H.-J. Werner, Simplified CCSD(T)-F12 methods: Theory and benchmarks,
JCP 130, 054104 (2009).